1. Field of the Invention
The present invention relates to a new toner for developing electrostatic latent images in electro-photography, electrostatic recording and electrostatic printing, and to a charge-giving member contributive to charge-giving to the toner in an image-forming process.
2. Description of the Prior Art
The development of an electrostatic latent image is carried out by causing a negatively or positively triboelectrically charged toner to be electrostatically adsorbed onto an electrostatic latent image formed on a photosensitive member. Then, the toner image is transferred onto a transfer paper and fixed.
Such a toner for developing a latent image is first of all required to have a reasonable amount of charge in order to provide a clear copy image which is free of fogs or the like. Further, it is required that the toner be not liable to change with time in its charge level, nor be it subject to such changes as noticeable charge decrease and solidification, due to environmental changes including, for example, temperature changes. As the charge decreases from the initial set value to an unreasonably low level, toner-scattering will increase, resulting in troubles, such as ground fogging, toner-scattering to white paper ground, and toner stains in a developing unit and associated surfaces.
In order to meet the foregoing requirements, a charge controlling agent is usually added during the process of toner making. Recently, with the advance of color copy, the development of white or light yellow charge controlling agents having good color reproducibility has been required.
At present, negative charge controlling agents, in colorless, white and light yellow, which impart a negative charge, are commercially available, but almost all of these agents are compounds containing a metal element, more particularly a heavy metal, for example, chromium-containing complexes or salts. Therefore, from the standpoint of safety, metal-free negative charge controlling agents which contain no heavy metal have been desired.
Whilst, recently there has been a demand for size reduction with respect to a developing machine in order to encourage the size reduction, price reduction and/or multi-color in copying machines. Further, from the standpoint of maintenance-free requirements, a unit of the developing machine is demanded. Because of these needs, a so-called single-component developing system has been paid attention to, which system is such that a thin toner layer is formed on a developing sleeve and the layer is brought into contact with a photosensitive member for development. However, unlike a two-component system in which a toner and a carrier are mixed in agitation for charging, the single-component system has a problem such that the time for toner charging is limited to a momentary time period in which the toner passes through the space between a layer-thickness levelling blade and the sleeve. As such, it is difficult to achieve any sufficient and uniform toner charging.
In view of this difficulty, it has been proposed to enhance charge giving to the toner by means of a transferring member, levelling member and/or friction member, for example, sleeve, doctor-blade, and carrier, which come into contact with the toner during the developing process, rather than attempting to achieve improvement in the toner-charging characteristics only through additives. However, above enumerated members are not only required to have high charging capability but also they must have high frictional resistance relative to the toner and good durability. For example, the carrier is required to be serviceable for a long time without replacement, and the sleeve is required to have the same degree of durability as the developing apparatus. In order to meet these requirements, attempts have been made to improve the charging characteristics of the toner by adding a specific charge controlling agent to the carrier, sleeve, doctor blade, etc.
In the present invention, members, such as transferring member, regulating member and friction element, are collectively referred to as "charge-giving member" to mean any and all materials and/or members which come in contact with a toner in a developing stage or prior to that stage to impart necessary electrical charges for development to the toner or supplementarily impart electrical charges to the toner.